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Caution:
Please read our safety
information before attempting any testing, maintenance
or repairs.
In every home is a drain, waste & vent system,
also called DWV. This drainage system is designed to carry
away waste water while preventing the flow of sewer gases into
your home. Some homes have a gray water system that has a
drain line for sinks, showers, dishwasher
and laundry and a separate black water line for toilets.
The gray water can be used for irrigation and toilet flushes.
Water flows down hill. The whole DWV system
is built on this principle and so most drain systems are gravity
flow systems. Each drain in your home travels down to a larger
branch drain. All the branch drains connect to a waste stack,
a vertical pipe that carries water to the main drain or sewer
line. A large pipe leaves your home and leads to the city sewer
or your own septic system. All of this is downhill, all the
way to the sewer or septic. In some cases, a home's sewer line
will be below the level of the city sewer, or a basement bathroom
is below the home's main sewer line and so pump equipment must
be used to move the waste out to the main sewer or septic.
All fixtures and appliances have a trap. A trap
keeps a few ounces of water at a low spot in the pipe to seal
the drain. This plug of water prevents sewer gas from traveling
through the pipes and into your home. An example of a trap
is the "P-trap" found under a sink. The water runs
through the drain and through the trap. The last few ounces
remain behind in that trap. It fills
the pipe and so prevents sewer gas from getting into your home.
Toilets have there own trap built right into the fixture.
Along with all
the drain and waste pipes, there is a system of vent
pipes integrated into the drain system. These vent pipes allow
sewer gas to be vented out above your home where it can quickly
mix with the air and dissipate. The vents also serve the important
function of preventing a vacuum or siphon from occurring. Because
water traveling through the pipes would create a siphon effect,
the water in the traps would be pulled along leaving the traps
empty, allowing sewer gas to enter the home. Also, if a vacuum
occurs, the draining water slows down much like how water gurgles
out when poured from a bottle. This slower moving water results
in the greater likelihood of clogging. A vent system is necessary
for the proper operation of a drain and waste system. Each
fixture must be properly vented and so a vent line branches
off of the drain line, to either join up to the main vent or
vents directly up through the roof.
The gravity system works well, unless something
impedes the flow of draining water. Swiftly moving water carries
waste away. However, if water cannot move swiftly, then the
whole system starts to fail. First waste builds up, further
slowing water flow until nothing is moving. The initial problem
that results in this cascade effect may be simply inappropriate
waste being sent down the drain. It can result from dips developing
in the drain line as the result of earth settling. Deterioration
of the drain pipes can result in rough surfaces that snag toilet
paper, which builds up, eventually clogging the line. Tree
roots grow through pipe fittings and also snag waste. Another
problem is putting grease, sand, coffee grounds and other "coagulants" down
the drain. While coagulants may not be a plumbing term, it
conjures the image of exactly what is happening. Things like
sand and grease tend to rest on the bottom of the pipe and
aren't easily washed away. They just coagulate and build
up over time.
The DWV system is really pretty simple. It has
some important refinements and the system has to be put together
well, with attention to details. However, it should not be
intimidating to you because in the end, it is a bunch of pipes
running downhill.
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